The invention relates to a master disc for the manufacture of matrices which in turn are used in the manufacture of optically readable information carriers, which master disc contains a substrate plate which is provided on one side with a layer of a radiation-sensitive substance in which an optically readable information track is provided.
Such a master disc is described in, for example, British Patent No. 2,128,206 (PHN 10.790) in the name of the Applicants. The layer of a radiation-sensitive substance used in the known master disc is a photoresist layer and, more in particular, a layer of a positive photoresist material. The optical information track is provided in this layer by patterned exposure of the layer, for example, by irradiation through a mask having apertures or by means of laser light which is modulated in accordance with the information to be recorded. The exposure is followed by a development step in which a developing liquid is used in which, in the case of a positive photoresist, the exposed portions of the resist layer dissolve or in which, in the case of a negative photoresist, the non-exposed portions dissolve. In general, the developing liquid is an aqueous alkaline solution which contains, for example, NaOH and Na.sub.4 P.sub.2 O.sub.7..sub.10 H.sub.2 O. After the development step a conductive layer such as a thin metal layer of Ag or Ni is applied to the photoresist layer by means of an electroless deposition process such as a vapour-deposition process, a sputtering process or a chemical plating process. A (further) metal layer such as, in particular, an Ni layer is provided on the conductive layer by electrodeposition, i.e. electrolytically, after which the master disc is separated from the metal matrix thus manufactured. Further metal copies can be made of the matrix, which are employed in the manufacture of optical information carriers.
European Patent Application No. 0224312 (PHN 11.563) describes a master disc which also contains a substrate plate, such as a glass plate, carrying a layer of a photoresist in which an information track is provided by exposure and developing. In an electroless deposition process the photoresist layer is subsequently provided with a metal layer to which a layer of a liquid, curable synthetic resin composition and metal supporting plate are applied. After the synthetic resin composition has cured by exposing it to for example UV-light, the supporting plate and the cured synthetic resin layer connected thereto are separated from the master. The supporting plate and the cured synthetic resin layer containing a copy of the information track of the master is used as a matrix in the manufacture of optically readable synthetic resin information carriers.
The master known from the above-stated literature references has the disadvantage that its manufacture comprises a great number of process steps, among others, a separate developing step.
A further important disadvantage is that the quality of the information track cannot be checked immediately. Quality control takes place at a later stage after a metal layer has been applied or the matrix has been removed from the master disc. In this process the master disc is lost due to damage to the photoresist layer.